1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef NETUTILS_SLICE_H
18#define NETUTILS_SLICE_H
19
20#include <algorithm>
21#include <array>
22#include <cstring>
23#include <ostream>
24#include <tuple>
25#include <vector>
26
27namespace android {
28namespace netdutils {
29
30// Immutable wrapper for a linear region of unowned bytes.
31// Slice represents memory as a half-closed interval [base, limit).
32//
33// Note that without manually invoking the Slice() constructor, it is
34// impossible to increase the size of a slice. This guarantees that
35// applications that properly use the slice API will never access
36// memory outside of a slice.
37//
38// Note that const Slice still wraps mutable memory, however copy
39// assignment and move assignment to slice are disabled.
40class Slice {
41  public:
42    Slice() = default;
43
44    // Create a slice beginning at base and continuing to but not including limit
45    Slice(void* base, void* limit) : mBase(toUint8(base)), mLimit(toUint8(limit)) {}
46
47    // Create a slice beginning at base and continuing for size bytes
48    Slice(void* base, size_t size) : Slice(base, toUint8(base) + size) {}
49
50    // Return the address of the first byte in this slice
51    uint8_t* base() const { return mBase; }
52
53    // Return the address of the first byte following this slice
54    uint8_t* limit() const { return mLimit; }
55
56    // Return the size of this slice in bytes
57    size_t size() const { return limit() - base(); }
58
59    // Return true if size() == 0
60    bool empty() const { return base() == limit(); }
61
62  private:
63    static uint8_t* toUint8(void* ptr) { return reinterpret_cast<uint8_t*>(ptr); }
64
65    uint8_t* mBase = nullptr;
66    uint8_t* mLimit = nullptr;
67};
68
69// Return slice representation of ref which must be a POD type
70template <typename T>
71inline const Slice makeSlice(const T& ref) {
72    static_assert(std::is_pod<T>::value, "value must be a POD type");
73    static_assert(!std::is_pointer<T>::value, "value must not be a pointer type");
74    return {const_cast<T*>(&ref), sizeof(ref)};
75}
76
77// Return slice representation of string data()
78inline const Slice makeSlice(const std::string& s) {
79    using ValueT = std::string::value_type;
80    return {const_cast<ValueT*>(s.data()), s.size() * sizeof(ValueT)};
81}
82
83// Return slice representation of vector data()
84template <typename T>
85inline const Slice makeSlice(const std::vector<T>& v) {
86    return {const_cast<T*>(v.data()), v.size() * sizeof(T)};
87}
88
89// Return slice representation of array data()
90template <typename U, size_t V>
91inline const Slice makeSlice(const std::array<U, V>& a) {
92    return {const_cast<U*>(a.data()), a.size() * sizeof(U)};
93}
94
95// Return prefix and suffix of Slice s ending and starting at position cut
96inline std::pair<const Slice, const Slice> split(const Slice s, size_t cut) {
97    const size_t tmp = std::min(cut, s.size());
98    return {{s.base(), s.base() + tmp}, {s.base() + tmp, s.limit()}};
99}
100
101// Return prefix of Slice s ending at position cut
102inline const Slice take(const Slice s, size_t cut) {
103    return std::get<0>(split(s, cut));
104}
105
106// Return suffix of Slice s starting at position cut
107inline const Slice drop(const Slice s, size_t cut) {
108    return std::get<1>(split(s, cut));
109}
110
111// Copy from src into dst. Bytes copied is the lesser of dst.size() and src.size()
112inline size_t copy(const Slice dst, const Slice src) {
113    const auto min = std::min(dst.size(), src.size());
114    memcpy(dst.base(), src.base(), min);
115    return min;
116}
117
118// Base case for variadic extract below
119template <typename Head>
120inline size_t extract(const Slice src, Head& head) {
121    return copy(makeSlice(head), src);
122}
123
124// Copy from src into one or more pointers to POD data.  If src.size()
125// is less than the sum of all data pointers a suffix of data will be
126// left unmodified. Return the number of bytes copied.
127template <typename Head, typename... Tail>
128inline size_t extract(const Slice src, Head& head, Tail... tail) {
129    const auto extracted = extract(src, head);
130    return extracted + extract(drop(src, extracted), tail...);
131}
132
133// Return a string containing a copy of the contents of s
134std::string toString(const Slice s);
135
136// Return a string containing a hexadecimal representation of the contents of s.
137// This function inserts a newline into its output every wrap bytes.
138std::string toHex(const Slice s, int wrap);
139
140inline bool operator==(const Slice& lhs, const Slice& rhs) {
141    return (lhs.base() == rhs.base()) && (lhs.limit() == rhs.limit());
142}
143
144inline bool operator!=(const Slice& lhs, const Slice& rhs) {
145    return !(lhs == rhs);
146}
147
148std::ostream& operator<<(std::ostream& os, const Slice& slice);
149
150}  // namespace netdutils
151}  // namespace android
152
153#endif /* NETUTILS_SLICE_H */
154